GRB 070721: Swift detection of a possible burst. Ziaeepour, H. ; Barthelmy, S. D. ; Beardmore, A. P. ; Burrows, D. N. ; Evans, P. A. ; Page, K. L. ; Troja, E. Abstract Publication: GRB Coordinates Network Pub Date: 2007 Bibcode: 2007GCN..6639....1Z